1. Field of the Invention
This invention relates to a benzoic acid derivative having a large positive dielectric anisotropy value, used as a component of liquid crystal materials, and a liquid crystal composition containing the derivative and having superior characteristics.
2. Description of the Related Art
Liquid crystals have recently been becoming very important as dielectrics for display devices. The reason consists in an electrooptical effect based on the dielectric anisotropy and optical anisotropy of liquid crystal substances. Display modes based on liquid crystals include various modes such as those of dynamic scattering type, twisted nematic type, super twisted nematic type, phase transition type, DAP type, guest-host type, etc. While the properties required for liquid crystal substances used for liquid crystal display vary depending on the respective liquid crystal display modes, a broad mesomorphic range and stability to moisture, air, heat, electricity, etc. are required for any display modes in common therewith. Further, when liquid crystal substances are used for liquid crystal display devices, it is also desired therefore to have a quick response of display elements and to be able to drive the devices under a voltage as low as possible. At present, however, there is no single compound which satisfies all of these requirements, but actually, several kinds of liquid crystal compounds or liquid crystal mixtures obtained by mixing several kinds of liquid crystal compounds with compounds having potentially liquid crystal properties or non-liquid crystal compounds have been used. Thus, it is also required that liquid crystal compounds have a good compatibility with other liquid crystal compounds.
As components of liquid crystal materials, the following ester compounds having a positive dielectric anisotropy value are enumerated:
compounds expressed by the formula ##STR3## wherein R represents an alkyl group (disclosed in Japanese patent application laid-open No. Sho 60-45549/1985), PA0 compounds expressed by the formula ##STR4## wherein R represents an alkyl group (disclosed in Japanese patent application laid-open No. Sho 59-193848/1984), PA0 compounds expressed by the formula ##STR5## wherein R represents an alkyl group (disclosed in Japanese patent application laid-open No. Sho 60-45549/1985), and compounds expressed by the formula ##STR6## wherein R represents an alkyl group (disclosed in Japanese patent application laid-open No. Sho 62-63549/1987). PA0 (1) a benzoic acid derivative expressed by the formula ##STR7## wherein R represents an alkyl group of 1 to 10 carbon atoms and A represents ##STR8## (2) a liquid crystal composition comprising at least two components at least one of which is a benzoic acid derivative of the formula (I) as set forth in the above item (1).